You'll need patience. You'll also need a formula worked out that works for the lower leagues i.e. right players, right tactic, right squad management. You'll find very quickly that playing extravagant formations and barcelona esque possession football won't work as the players you can get hold of just aren't technically gifted enough to replicate it.
Physical attributes are everything. Pace and acceleration destroys in the lower leagues. If you can get some strikers with high stats in these and even finishing and composure at least 10....then that will provide a big step towards promotion. Simple 4-4-2 should do the trick.
I'm implementing the advice in the "understanding odds" thread and am having solid results. Experience over youth tends to be the best way, but if you can get good youngsters in then all the better.
Plenty of threads about and videos on you tube to sink your teeth into.
Something I discussed in a thread I made yesterday. Make sure to have the lowest divisions for the countries you want in your game loaded up. Or you'll get interest from top level teams, e.g. I had only the top Russian division loaded up and was accepted by Dynamo Moscow, which obviously was far from realistic for a sunday league rep manager. If you're really looking for realism, you'll want to remember this.